1. Field of the Invention
The present invention relates to a novel control unit for driving and controlling a plurality of loopers, and particularly to a control unit for comprehensively controlling a plurality of loopers having different amounts for transferring the same and different strand numbers.
2. Description of the Prior Art
Generally, in an installation for processing strip-like materials or the like, it is required to join the succeeding material to the preceding material by means of welding or the like in order to perform continuously such processing. For this reason, operation in such installation for processing must be stopped because of working for cutting, welding and the like of the strip-like materials. Thus, for the sake of making continuously the following principal working such as the processing itself and the like possible during stop of supplying such material, a loop or loops are disposed on the route of transferring material in the installation.
Formerly, such loop was a free loop to which no tension had been applied, but in such free loop, meandering of a material or the like became remarkable in the case where speed of transferring the material was particularly high so that problems occurred frequently.
Recently, however, tension loops being loopers such as loop cars or the like have been utilized.
For simplicity, an example in which a loop car is utilized as a looper will be described hereinbelow. FIG. 1 is a system diagram showing a conventional control unit for driving a single loop car in which each loop car 5 of two strands is driven by means of one rope. And these two ropes are wound around one rope drum 3 so that four strands are simultaneously controlled in this unit.
Meanwhile, a purpose for the use of such loop car resides in that a difference in speed between its processing section and an adjacent section, in other words, the difference between the processing section and its inlet or outlet section is absorbed. For this reason, the loop car is disposed in between the processing section being continuously operated and a section where the operation is stopped for welding or dividing a travelling material. Accordingly, a strip 7 stored in the loop car is supplied to the processing section during stop of the operation. On the other hand, when the operation is started, a speed of the inlet section is adjusted to make it higher than that of the processing section, thereby storing the strip 7. When the strip 7 stored in the loop car reaches to a certain amount, the speed of the inlet section is synchronized with that of the processing section, and the operation is again stopped for welding the travelling material. Although the above explanation was made upon such a case where a loop car is placed on the inlet side of the processing section, such a case where another loop car is placed on the outlet side thereof will be also easily understood. As described above, loop cars are an important apparatus being indispensable for continuous processing line.
Next, a construction of a conventional unit as shown in FIG. 1 will simply be described hereinbelow. In FIG. 1, reference numeral 1 designates a bridle motor on its inlet side, while numeral 2 designates another bridle motor on the outlet side, and these motors control speed in each section. Reference numeral 3 designates a drum around which two wire ropes are wound, and loop cars 5 placed on the upper and lower stages are arranged in such that these loop cars are travelled on rails (not shown) by means of the wire ropes extending from the drum 3, respectively. The strip 7 being a travelling material is in four strand form by means of the loop cars 5 in two stages. The drum 3 is driven by a motor 8. Furthermore, each speed of the motors 1, 2 and 8 is detected by means of speed generators 10a, 10b and 10c, respectively. Moreover, reference numeral 13 designates a power unit for the driving motor, 14 a torque controlling circuit, 15 a speed dead band, 16 a speed controlling circuit, 20 a speed command circuit, and 22 a tension presetting means, respectively. Tension of the loop cars 5 is preset by means of the tension presetting means 22, and travelling speed of the loop cars 5 is determined by a difference in speed between the bridle motor 1 on the inlet side and the bridle motor 2 on the outlet side. Namely, the loop cars transfer towards the right side in the drawing, respectively, in the case where a speed of the motor 1 is faster than that of the motor 2, whilst the loop cars transfer towards the left side in the drawing, respectively, in the case where a speed of the motor 1 is slower than that of the motor 2, Furthermore, the loop cars stop in the case where speeds of both the motors 1 and 2 are equal to each other.
As mentioned above, important functions which should be possessed by the loop cars are that there is a large amount of the strip 7 stored, that there is found a little meandering of the strip 7 in the loop cars, and that there is a little fluctuation of tension at the time of starting and stopping the unit. However, with growing speeding up of continuous processing line, there is a limit in a driving means for a single loop car in order to satisfy important functions of the loop cars as described above. Thus, it is required to provide a driving means for plural loop cars. More specifically, the detailed reasons required for providing such driving means for plural loop cars are as follows.
There are two ways for increasing an amount of the stored strip in a single loop car; either the number of strands is increased or an amount of the loop car travel is increased. However, these two ways have also the following disadvantages.
Increase in number of strands brings about increase in bending loss as well as mechanical loss of a strip. Therefore it is required to increase difference in tension between the strip positioned on the uppermost stage and the strip positioned on the lowermost stage. In this respect, it is impossible to increase the difference in tension as mentioned above in a driving means for a single loop in which the whole strands are controlled in a lump. On the other hand, such way in which amount of the loop car travel is increased without increasing number of strands accompanies increase in mechanical loss, and after all, this way has also the disadvantages as mentioned above. Besides, stable operation becomes impossible, because meandering of the strip is amplified in these ways.